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Trainer rides leaving you exhausted? Here’s what every cyclist needs to know about dehydration.

Updated: Jan 31, 2022

Love it or hate it, for many of us are training in the "pain cave" for the next few months.

Your bike is set up inside on the trainer or rollers, towel draped over the bars, motivational quotes taped onto the wall and a side table (or upside-down laundry basket?!) is set up beside the bike for your training nutrition and hydration. And you have a fan to stay cool, or do you?

Staying cool in the dungeon can contribute to going the distance, without finishing feeling trashed.

Professional Cyclists Lex Albrecht is dialed in with her fan, 2x 750ml bottles and she is hard core, no screen here, just a workout to hammer out and a laser focus!

As athletes, our body’s cooling mechanisms play an important role in our ability to sustain prolonged efforts. When we exercise, we increase our metabolism and the energy we expend. This energy is mostly produced as heat. The body has mechanisms to help regulate heat and manage our core body temperature as best as possible, sweating being one of them, as it evaporates from your skin's surface, it removes heat, cooling us off (although high humidity challenges this).

Several things factor into how much you sweat, including your clothes, exercise intensity, environment, hydration status, possibly your sex, and even how acclimated you are to the heat. If you're training in your basement, consider this your ‘environment’. Room temperature is rather warm, and the air is quite stagnant. Adding ‘wind,’ by use of a fan, can help to cool you off in your indoor training environment.

Most athletes won’t replace all the sweat they lose during prolonged sessions, and this is normal. In fact, some studies suggest we may be able to acclimate to dehydration, although this is currently an ongoing area of research and somewhat controversial. You can read more about this and how research methodology plays into the conversation in this review.

Although sweat losses don’t always result in impaired performance, the longer you ride, the larger those losses can become.

Several studies have shown losses as little as 1% and greater than 2% of your body mass, can impair cycling performance (less power output).

You can prevent some of these losses through hydration and cooling strategies.

We all have individual sweat rates, some athletes lose as little as 1L/hour while some trained athletes, including marathon runners, lose 4L/hour. Understanding your own sweat rates is important when creating a personalized hydration strategy.

If you are a heavy sweater, and maybe also a heavy salt sweater, you’ll need to pay attention to that pre-post-training body mass loss even more closely.

What's happening when you become dehydrated?

From a cardiac (heart) perspective, when you have prolonged sweating, your blood volume drops. Blood is made up of 55% plasma, and the plasma portion of your blood is 90% water, hence the resulting loss in blood volume with water losses. As a result, your heart needs to pump harder to distribute this smaller volume of blood throughout your body each minute. Since its blood that brings oxygenated blood to your working muscles, your body is now working harder to be able to do this.

Cardiac output (CO) is the amount of blood in liters that your body pumps throughout your systemic circulation. Stroke volume (SV) is the volume of blood that is pumped out of your left ventricle from your heart, during each heart contraction. Heart rate (HR) is the rate that your heart pumps, for example, 60 beats per minute.

CO = SV x HR

(to maintain the same CO your heart rate would have to increase, if you decreased stroke volume due to plasma losses from sweat).

Imagine trying to fill a tire with a tiny pocket pump (smaller SV) versus a large floor pump (larger SV), it’s a lot more work to use the pocket pump. Compare that to your heart beating faster (HR) to get enough oxygen throughout your systemic circulation per minute (CO). It’s harder work!

Depending on your cycling pace, this higher heart rate will become more difficult to sustain as time passes.

Imagine working at 140 beats per minute versus 150 beats per minute, at the same wattage. Your body is now under more stress, not due to a change in strain (ex. wattage) but from the dehydration and these trickle-down cardiac effects. This leads to more unnecessary fatigue. Not only is the workout physiologically harder, but you also have an increased perception of exertion which can wear on you psychologically. Unless you purposely heat adapt, this added stress isn’t beneficial.

Here's the good news. By setting up a fan and having a hydration strategy, you can prevent some of these consequences. Also keep in mind that the fitter you get, the more efficient you'll become at sweating, as your sweat response becomes more developed. Keep on training!

General hydration guidelines:

Although the jury is out as far as precise goals for hydration status from pre/post-training, the most current recommendations from several resources are to keep water losses due to exercise and lack of hydration below 2% of your body mass.

Here are a few tips that can help:

  • Enter an exercise session in a hydrated state. If you start dehydrated, you’re already behind the 8 ball.

  • Look for a pale-yellow color of urine and consider drinking 500-1000ml of water 3-4 hours pre training, as well as drinking based on thirst throughout the day.

  • During your ride, aim for 500ml/hour. Adjust upward if you're a heavy sweater and use a sports drink for prolonged rides over 75-90min.

  • Start your day with a full 1L bottle and drink it twice by the day’s end, in addition to your hydration during training. (Many athletes will consume more than this)

  • TIP! Fruits and vegetables contain a lot of water too. Carrots, cantaloupe, strawberries, cooked squash are all over 90% water!

If you weigh yourself pre and post ride (without clothes on) and notice you’ve lost 4% of your body mass during that time (if you weight 130lbs that 5.2lbs wat